1. Field of the Invention
The present invention relates to a device for viewing the inside of a mouth, namely a device permitting to see an inner portion located under an outer surface of an organ arranged in the mouth.
2. Description of Related Art Including Information Disclosed under 37 CFR 1.97 and 37 CFR 1.98
The known devices aimed at viewing in the field of dental treatments of the invisible sub-gingival, coronary, radicular or osseous parts include the following devices:                a penetrating ray emitter such as an X-ray device operating in 2D (conventional radiography or radiovisiography), in 2D½ or 3D (scanner, cone beam, panoramic scanner or orthopantomograph) or an MRI device, an ultrasound device, a device operating with terahertz radiation or a device operating with the techniques derived from the holographic interferometry (OCT);        eventually an intraoral camera for taking an impression by optical means (radiation ranging from deep blue to X-ray, even ultrasound), whether using a structured projected light or not; and        a remote display screen permitting to see, on the one hand, the view of the modeling from the device emitting penetrating rays and, on the other hand, the modeling obtained as a result of the scanning performed using the intra-oral camera displayed after the clinician has performed the optical impression.        
Radiology devices used in dental treatments can be divided into two large categories, those located close to the dental unit and the remote ones.
In the first category we find devices using silver-based, phosphor-based or digital supports (radiovisiography or RVG).
Though the silver-based devices are increasingly less used, this is not the case for the other two, since they permit to scan indirectly (phosphor-based supports) or directly (RVG) the pixelated radiological image obtained from osseous tissue by transparency to X-rays. In both cases, the image obtained is scanned in grayscale and displayed in 2D on a screen near the practitioner, in black and white or in reconstructed virtual colors. This image allows him to know the sub-gingival condition of the osseous tissue, but also of the crowns and roots of the teeth.
The clinician carries over and intuitively matches the viewed shapes seen on the 2D screen onto the parts visible in the mouth of his patient. This allows him to have a very rough idea of knowing the shape and length of a root, of knowing whether there are pathological pictures and to imagine the position of the nerves and the big blood vessels. If he also wants to monitor over time whether his treatment is effective or not, he will have to make several successive pictures.
With the emergence of a more demanding dentistry, in particular addressing the treatments in periodontology and implantology, more complex devices, which represent a second category, have been used. These devices are rarely present in the dental office, but they allow the dentist to have a general view of the entire mouth in 2D, 2D½, even 3D if he uses magnetic resonance (MRI).
In this category we have found over the last thirty years the oral scanners (pantographs, panoramic scanners) providing 2D images of the entire arch in one picture, the CT scanner providing 2D½ images that permit, thanks to the different voxel planes, to reconstruct a false 3D image (scanner) and more recently the cone beams combining the advantages of the traditional scanner and the CT scanner providing a very fast and much more accurate 2D½ picture of the osseous tissue.
The latter images are widely used in implantology where the practitioner should exactly know the position of the underlying organs such as the sinuses and the various osseous structures when preparing the site for receiving his future implant.
In all cases, these spatial 2D½ (or false 3D) images are shown on a remote 2D screen permitting to move them in three planes in space and to know where the interesting areas or risk areas are located.
Finally, some practitioners use real 3D images in MRI, but this is still seldom and very expensive. In this case too, the display will occur on a remote monitor.
Recently, and in view of the inaccuracy of the radiological image, some clinicians have decided to associate with the inaccurate X-ray image (100 to 200 microns) a much more accurate (10 to 30 microns) image of the outer portion obtained using an intraoral camera for optical impression. By blending the first and the second image, they get on the remote 2D screen a combined view of the tissues and the underlying organs and the optical impression of the teeth and the gums.
Unfortunately, though the knowledge of the proximity of an underlying organ is acceptable to within about one hundred microns, this is not true for the accuracy of a crown or the cylinder of an implant, which must be known to within about ten microns.
If they use the systems described above for the sub-gingival view, they need in addition an optical impression camera in order to have a sufficiently accurate external view.
Nowadays, as a direct result of the works by the inventor François Duret, there exist different kinds of methods for taking an intraoral optical impression in the dental practice, which can be combined in a radiological image. We find:                those projecting onto the tooth a structured light, which may be a dot, a line or a complete grid. They have been widely known for several decades and are very well described in the article by G. Hausler and Col “light sectioning with large depth and high resolution” in Appl. Opt. 27 (1988). They can use, for example, projections of grids with variable pitch (“numerical stereo camera” SPIE Vol 283 3-D, 1981), the principle of the profilometric phase (Duret U.S. Pat. No. 5,092,022 and U.S. Pat. No. 4,952,149), the best known of which is the CEREC (Sirona GmbH), the one that combines the projection of the fringe and phase variations of the Hint-Els Company (USA) or the parallel confocal principle such as the Itero (US.0109559) from Cadent (USA).        those that do not use the projection of active or structured light, but the stereoscopic interferometry. This is the case of the Lava AWS camera from 3M (Rohaly and Co, U.S. Pat. No. 7,372,642) or the Condor camera from Duret and V & O Querbes (U.S. Pat. No. 8,520,925).        
Though we can say that all these works and inventions have led to many embodiments and to more than twenty commercially available systems (F. Duret, dental floss No. 63, May 2011, “the great adventure of the CADCAM at the IDS in Cologne” 14-26), none of them has provided an original solution permitting to display the impression of the visible and invisible parts directly in the mouth during and after their taking.
All these described methods, implemented in dental offices or in another room for large radiology devices, use the same display system: a remote screen close to or far away from the operator. Irrespective of the complexity of these devices, with all the cameras or radiology devices that we have described above is associated a screen. It can be placed on a kart, be connected to or depending (all-in-one) on a computer or be part of or the whole laptop or tablet.
In the case of a data-processing monitor (video, plasma, LCD or LED). The screen is specific to the application, radiological or display of the optical impression being taken. Sometimes it combines the two methods (Planmeca, Carestream) by displaying in two different windows the video picture from the camera view and the modeled picture resulting from the radiological and/or intraoral digital processing.
On this same screen can be displayed the practitioner's interactive view that permits him to complete the information relating to the patient: the medical characteristics and the care to be brought or already brought. This is referred to as the patient card. In this case, it is no problem to display this information on a remote screen, since the elements contained in this card are rarely completed during the actions or need not be displayed during same. Although this has already led to making an augmented-reality application, for us it is of little interest to the patient's health. This is not case as regards the displaying of his physiological data during the intervention, as we will see in the accessory applications of our invention.
The digital central processing unit (CPU) collects and processes the information proceeding from the intraoral camera and the radiology devices, then displays them on the display screens.
We immediately understand that the first problem faced by the operator is to have to look on one or more remote screens at the radiological view and the one proceeding from his intraoral camera. If he uses a silver-base support, he has no option but to use a light box. This obliges him to look away and to never have any accurate match between his clinical space, which is what he sees in his patient's mouth, and the sub-gingival area, which is radiologically known and displayed on the monitor.
We understand why the clinician must constantly take his eyes away from his operating field to the remote image.
In addition, though he is provided with augmented-reality indications on the remote screen, he must not only make the effort of moving his eyes from his operating field to the monitor, but also of transposing with his brain and virtually these indications and information displayed on the remote 2D screen to the operating field, with the risk of being inaccurate or of doing it wrong.
This is extremely uncertain, especially since the only region corresponding to a common volume between the visible part and the sub-gingival part permitting a correlation by the mind is in the radiological view displayed in 2D on the screen, while in the mouth his vision is three-dimensional. The operation is so inaccurate in implantology that the clinicians must use guides, which are secured to the teeth, so that their drill bits do not injure the underlying tissue.
We easily understand that seeing indirectly the course and the result of his work is dangerous for the patient, inaccurate, incomplete and extremely damaging in daily practice. We can summarize the issues arising from this way of displaying on a remote screen as follows:                this obliges the latter to permanently move his eyes between the body part on which he is working and the remote screen. Indeed, if the practitioner wishes to follow the evolution of his endodontic or surgery work, he must move his eyes away from the body area on which he is working and watch his video or digital screen (monitor) in order to guess where his work is located,        this movement can lead to adverse, inaccurate and uncontrolled movements of his hands during his work, which issue is especially important when he works for a long period (fatigue),        this movement is dangerous because his eyes regularly leave the operating field at the risk of causing an injury in the patient's mouth or body or of breaking his instruments.        this is also very tiring because the existence of a remote display requires eye gymnastics at a very high pace. It is thus possible to have more than 20 to-and-fro movements of his eyes per minute.        
This excludes any additional directly correlated information about the viewed field as is now possible with the augmented reality. Having no correlation between the actual view and the information proceeding for example from the augmented reality on a remote screen excludes any real time and any accurate information in the operating field. Even though this information appears on the remote screen, the display will never be in real time and the clinician's gesture will not be positioned accurately in the working field.
This action is inaccurate: we see that though it is possible to see the underlying tissues on a remote screen, the direct viewing of his work is never secure, because moving his eyes and changing the clinical action area during his work makes difficult the correlation between the two observations. There exists no real correlation between the RX representation and the working field, due to the use of the remote screen. This also applies to any information from the augmented-reality software transferred onto the remote screen.
This operation is insufficient: the RX radiation produces a 2D or 2D½ display transferred onto a 2D screen, which makes it especially difficult, even impossible, to estimate what has been x-rayed with respect to what is actually present in front of the operator in 3D eye vision.
This medical procedure is not secure: we can say that no simple and especially secure solution has been found to meet the needs of the clinician. For his action to be secure, he must see the area that has been X-rayed and the area on which he is working combined in real time in one and the same repository. This is the essential condition for being able to work safely, quickly, with total comfort and with the accuracy required for this type of intervention.